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    Triode Electronics St-70 Driver Board Wiring Instructions Question

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    deathman68

    Posts : 10
    Join date : 2016-01-23

    Triode Electronics St-70 Driver Board Wiring Instructions Question

    Post by deathman68 on Sat Jan 07, 2017 9:01 am

    Hi all,

    It's been a while since I've posted. I've done a search but didn't come up with the exact answer I was looking for.

    I'm finally getting around to finishing up the wiring on my triode electronics St-70 driver board and have a doubt with regards to Note 1 for Eyelets #4, 5, 15, & 16. Per the instructions note 1 says:

    "NOTE 1: These are the input tube filament connections. A stock ST-70 uses the front panel power take-off sockets as a tie point for the input board tube filament wiring. Many amplifier modifications use these socket holes for input jacks or other purposes. If the tube filament power is not present on these jacks or the jacks themselves are not present, then the filament wiring can be run (as twisted pairs to reduce hum) from the output tube filament connection (EL34: pins 2&7). The phase inverter position (V2) now has extra flexibility to use tubes with different pinouts, to use 12AU7, 12BH7, ECC99 solder a wire from J1 to J2 and make your filament connections to eyelets 24 & 25, to use 6CG7, 6922, 7308, or 6DJ8 do not jumper J1 and J2 and instead make your filament connections to J1 and J2 and ignore eyelets 24 and 25."

    Specifically I'm planning on using a 12AU7 so per Note 1, I've jumpered J1 & J2 but am unsure about whether or not I should be connecting (or using) Eyelets #24 & 25 for the filament connections since filament power is already present on the front panel power take-off sockets. I've included a photo which shows how I currently have the board wired but wanted to confirm before powering up. I currently have 24 & 25 connected to the filament power for the left side only (eyelets 4&5 to pins 1&2 of the left power take off socket and pins 1&2 also wired to eyelets 24&25). Per the instructions I have eyelets 15&16 wired to pins 1&2 of the right power take off socket only.


    Hopefully it's clear what I'm asking. Thanks!

    Jeff
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    PeterCapo

    Posts : 407
    Join date : 2008-12-05

    Re: Triode Electronics St-70 Driver Board Wiring Instructions Question

    Post by PeterCapo on Thu Jan 12, 2017 9:34 pm

    deathman68 wrote:Specifically I'm planning on using a 12AU7 so per Note 1, I've jumpered J1 & J2 but am unsure about whether or not I should be connecting (or using) Eyelets #24 & 25 for the filament connections since filament power is already present on the front panel power take-off sockets.

    If the above excerpt is the crux of your question, I think you have it right per your photo.  If "...filament power is already present on the front panel power take-off sockets," it doesn't change the fact that the tubes on the PC board need you to make a filament connection to them.  The wiring at front panel socket pins 1 & 2 does not power the filaments for the tubes on the PC board unless you run the twisted pairs to the PC board, as you have done.

    You run twisted wire pairs either from the EL34 to the PC board or from the front panel sockets to the PC board, per the instructions.  They're the same nodes.  If you trace the wires at front panel socket pins 1 and 2, I believe you'll find that they come from EL34 socket pins 2 and 7.  When the instructions say "filament power is already present on the front panel power take-off sockets," it was originally also intended to provide filament power to certain preamps via an umbilical that connected between the front panel sockets and the preamp.

    Hope I understood your question.

    deathman68

    Posts : 10
    Join date : 2016-01-23

    Re: Triode Electronics St-70 Driver Board Wiring Instructions Question

    Post by deathman68 on Fri Jan 13, 2017 7:11 am

    Yes you understood the question perfectly. Last night I spent some time studying the pcb traces and came to the same conclusion. The wiring should be correct. Now the question becomes why are my voltages out of range and getting 0 volts despite bias potentiometer position on both sides?

    When I measured cap voltages on the SDS board they were all nearly zero so I'm suspecting either a faulty PA060 or dry solder joint somewhere. I'll troubleshoot this weekend and report back with specific voltages at bias, B+, etc. Thanks!

    deathman68

    Posts : 10
    Join date : 2016-01-23

    Re: Triode Electronics St-70 Driver Board Wiring Instructions Question

    Post by deathman68 on Sat Jan 14, 2017 4:43 pm

    Making *some* forward progress on this.  I realized I'm a bonehead and never grounded the cap board hence no previous voltage readings there.  Once I got the board grounded properly, I removed all tubes and measured the A060 voltages per the post found here:
    http://dynacotubeaudio.forumotion.com/t616-pa-060-bench-testing

    Surprisingly, all voltages were in range except for the green/yellow to red/yellow and brown/yellow to red yellow. Both of these read zero volts in spite of the correct ground, so perhaps its worth a deeper look?

    Then I installed my GZ34 rectifier tube and proceeded to measure the voltages at the various pins for the EF86's and my 12AU7.  Below is a summary table which I hope will clarify the situation some.

    https://i37.servimg.com/u/f37/19/59/72/86/st70_v10.jpg

    I'm thinking at this point that my wiring is probably ok and that I should start simple by figured out why the A060 isn't putting out the requisite voltage as I believe this is fundamental to the functioning of everything else.  I haven't included the EL34 voltages yet.  Any ideas?

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